Frequently, to reduce the amount of storage and computation required by digital video, the digital video is captured in a format in which the video data is compressed using inter-frame compression. MPEG is an example of a format that uses inter-frame compression.
MPEG is a popular standard that has been developed for digitally storing audio-visual sequences and for supplying the digital data that represents the audio-visual sequences to a client. In the examples hereafter, MPEG is used as an example of an inter-frame compressed format. However, MPEG-1 and MPEG-2 are merely two examples of inter-framed compressed formats with which the techniques described hereafter may be applied. The techniques are not limited to any particular inter-frame compressed digital format.
In the MPEG format, video and audio information are stored in a binary file (an “MPEG file”). The video information within the MPEG file represents a sequence of video frames. This video information may be intermixed with audio information that represents one or more soundtracks. The amount of information used to represent a frame of video within the MPEG file varies greatly from frame to frame based both on the visual content of the frame and the technique used to digitally represent that content.
MPEG employs three general techniques for encoding frames of video. The three techniques produce three types of frame data: Intra-frame (“I-frame”) data, Predicted frame (“P-frame”) data and Bi-directional (“B-frame”) data. I-frame data contains all of the information required to completely recreate a frame. P-frame data contains information that represents the difference between a frame and the frame that corresponds to the previous I-frame data or P-frame data. B-frame data contains information that represents relative movement between preceding I or P-frame data and succeeding I or P-frame data. These digital frame formats are described in detail in the following international standards: ISO/IEC 13818-1, 2, 3 (MPEG-2) and ISO/IEC 11172-1, 2, 3 (MPEG-1). Documents that describe these standards (hereafter referred to as the “MPEG specifications”) are available from ISO/IEC Copyright Office Case Postale 56, CH 1211, Genève 20, Switzerland.
As explained above, video frames cannot be created from P and B-frame data alone. To recreate video frames represented in P-frame data, the preceding I or P-frame data is required. Thus, a P-frame can be said to “depend on” the preceding I or P-frame. To recreate video frames represented in B-frame data, the preceding I or P-frame data and the succeeding I or P-frame data are required. Thus, B-frames can be said to depend on the preceding and succeeding I or P-frames.
Inter-frame compressed formats present a problem to video editors, because the removal or editing of one frame may affect or render unintelligible one or more other frames. Therefore, as a preliminary task before editing a video encoded in an inter-frame compressed format, the video is converted to a format in which the inter-frame dependencies are removed. For example, an MPEG encoded video may be converted to a format in which each frame is represented by a JPEG image whose content does not depend on the content of any other frame. Formats in which the inter-frame dependencies have been removed are referred to herein as independent-frame formats. Once in independent-frame format, a video may be edited without worry of creating problems related to dependencies between frames.
While a video is being converted from an inter-frame compressed format to an independent-frame format, it is often desirable to display the video that is being converted. Unfortunately, the overhead associated with converting and playing the video is such that many older computer systems are incapable of keeping up with the incoming video stream. This is particularly true if the video being converted is a high definition video that is being streamed to an older computer over a fast I/O connection. For example, a relatively older computer may not have the computational power necessary to convert an HDV stream, a format based on MPEG-2 transport stream with high definition MPEG-2 video and MPEG-1 layer 2 audio, as it arrives over a FireWire connection from an HDV camera.
As used herein, the term “high definition video” refers to any video format with higher resolution or frame rate than standard definition. For example, a frame dimension of 720×480 at 60 frames per second is high definition because it has a higher frame rate than NTSC. Most common high definition formats are 1280×720 at 60 frames per second and 1920×1080 at 60 fields (30 interlaced frames) per second. HDV is an example of one format that carries high definition video.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.